In general, as portable electronic devices such as video cameras, cellular phones, and portable computers have become lightweight and highly functionalized, a significant amount of research has been conducted into a secondary battery used as a driving source thereof.
The secondary battery may be, for example, a nickel-cadmium battery, a nickel-hydrogen battery, a nickel-zinc battery, a lithium secondary battery, or the like.
Among these, a lithium secondary battery is advantageous because the battery may be miniaturized and large and has high operation voltage and high energy density per unit weight and thus has been widely used in many fields.
In particular, in order to solve air pollution and so on due to a conventional gasoline vehicle or diesel vehicle using fossil fuel, research has been actively conducted in recent years into an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (P-HEV), and so on, which use a chargeable and dischargeable secondary battery.
Unlike small-size mobile devices, a medium-to-large size device such as a vehicle requires a high-output and large-capacity secondary battery, and thus uses a medium-to-large size secondary battery module formed by connecting a plurality of battery cells.
It is preferable to manufacture a medium-to-large size secondary battery module with as small as possible size and weight, and thus prismatic batteries, pouch-type batteries, and so on, which are stacked with a high integration degree and have a small weight compared with capacity have been mainly used as a battery cell of a medium-to-large size battery pack.
With the large-size battery pack, U.S. Patent No. 2013-0045401 discloses a battery pack comprising an electrode module formed by sequentially stacking a cathode plate, a separator, and an anode plate; a pouch for sealing the electrode module; a lead tab that is connected to the electrode module and is partially exposed out of the pouch; and a case for supporting one surface of the pouch in which the electrode module is sealed and one surface of the lead tab and including a terminal portion in which the lead tab is accommodated, wherein the terminal portion includes a first groove portion for attaching a temperature sensor thereto and a second groove portion for coupling a bus bar thereto.
However, according to the prior art, since swelling whereby a pouch billows due to overcharge of a battery pack may occur which causes a short circuit of an internal electrode, the battery pack is likely to ignite, and thus safety is not capable of being ensured.